1. Field of the Invention
The present invention relates to tube fittings and more particularly tube fittings for use with plastic tube which can be sealingly connected to the tube by pushing the tube into the tube fitting.
2. Description of the Prior Art
Push in plastic tube fittings which allow a tube to be sealingly connected to the fitting by pushing the tube into the fitting generally include a body, a gripper and an o-ring for sealing. The o-ring and the gripper are disposed in the body such that a tube can be pushed into the body through the gripper and then the o-ring. The o-ring is compressed between the exterior of the tube and the body to seal the connection therebetween. The gripper captures the tube and prevents its withdrawal from the body.
Push in plastic tube fittings for use with plastic tubing have generally included a gripper formed on the interior of a cylindrical collet with extends from the exterior of the body to a camming surface on the interior of the body. The interior of the collet has an enlarged cam section which bears against the camming surface of the body such that as the collet moves axially outwardly the gripper on the interior of the collet is moved radially inwardly by the camming action of the cam section on the camming surface. This radially inward movement of the gripper bears against a tube which is disposed in the collet. This prevents the tube from being withdrawn from the fitting since the withdrawal movement of the tube carries the collet and tightens the gripper on the tube by the cam action of the collet cam sections. Examples of push in tube fittings of the type described are shown in U.S. Pat. Nos. 4,005,883 to Guest; 4,606,783 to Guest; 4,650,529 to Guest; 4,722,560 to Guest; and 3,653,689 to Legris.
A problem with push in plastic tube fittings has been that the plastic tubes are scratched by the gripper mechanism as they are pushed into the fitting. The scratches on the tube cause leak paths which are poorly sealed by the o-ring which extends about the exterior of the tube over the scratches. These scratches are caused by the sharp edges of the gripper. Moreover, most grippers are formed of metal and the metal tends to have both sharp edges and imperfections which can cause scratches.
Another problem with push in plastic tube fittings has been that the metal elements of the gripper serve as a source of contamination to fluids in the tube. Some fluids which are conveyed in the tube and tube fittings are easily contaminated by metals and, therefore, it is desirable not to have any metal components in the fluid path or the fitting. However, the stresses placed on fittings, especially the gripper portion of the fittings are sufficiently severe that prior art fittings have generally included metals as the only solution for this demanding application.
Another problem with tube fittings of the prior art which have metal grippers and nonmetal collets is that it is difficult to form the collet of plastic with metal grippers therein. First, the metal portions of the gripper are small pieces and difficult to locate. Secondly, it is difficult to accurately orient the metal portions in the plastic collet. Still further, the shapes and orientation of the various pieces of the fitting have been difficult to manufacture and assemble.